Volcanic-origin soils, such as in the Pacific Northwest, are depleted of sulfur, a secondary but essential nutrient to plants.
Standard practice for applying sulfur to such soils by users of solid fertilizers has been the application of such as prilled ammonium nitrate-ammonium sulfate solid products, or the use of ammonium sulfate as a crystalline form, or the use of such as certain commercial/fertilizer grades of monoammonium phosphate 16-20-0 (N-P.sub.2 O.sub.5 -K.sub.2 O) which contain low levels of gypsum as impurity.
Another solution has been the approach of suspending pulverized gypsum and/or elemental sulfur in a high nitrogen liquid fertilizer. While this sounds attractive, on a practical basis it has disadvantages in plugging spraying nozzles, and the like, or sometimes tending to either settle out or induce crystallization of the liquid fertilizer.
Liquid fertilizers compete with the solid sulfur-containing fertilizers by use of various liquid sulfur products. Ammonium polysulfide, analyzing about 20 percent nitrogen and 45 percent sulfur, is not miscible with anhydrous ammonia but is commonly coapplied with anhydrous ammonia as a soil treatment by using inconvenient dual metering and application systems. Another material commonly employed is a concentrated ammonium thiosulfate solution 12-0-0-26 (S) which is compatible with aqueous ammonia, or with another liquid fertilizer UAN-32, allowing the sulfur in this fashion to be added with the nitrogen source as a single phase liquid system. However, this is disadvantageous in that the two materials frequently must be obtained from separate suppliers, and coadmixed by the user.
Liquid fertilizers do have the inherent advantage over solid fertilizers in being particularly suited and convenient for many agricultural applications. Liquid fertilizers can be easily applied by a variety of application methods at various readily controllable strengths to either the plant or soil surface or into the soil subsurface.
Of course, to minimize shipping and handling costs, storage volumes, etc., it is important to provide as highly concentrated a liquid fertilizer as feasible. A major disadvantage, however, of liquid fertilizers is that they are temperature sensitive, that is, they begin to crystallize out of solution as the solution temperature decreases, with 32.degree. F. (0.degree. C.) being considered an acceptable low temperature. Crystallization causes serious problems such as plugging of lines, applicator nozzles, storage tanks, etc., as well as reducing the nutrient value of the fertilizer. Consequently, liquid fertilizers generally are limited to use when the ambient temperature is above the crystallization temperature of the fertilizer solutions.
Thus, important is the development of liquid fertilizers that contain appreciable sulfur, but which will not crystallize during cold temperatures, particularly sub-zero temperatures. Such liquid fertilizers would not plug equipment and storage tanks, and of extreme importance the liquid fertilizers could be applied to the soil during the non-growing, less productive cold season (e.g. winter), thus, reducing labor time during the valuable growing portion of the year (e.g. spring), for the same fertilizer application.
Since most liquid fertilizers employ water as the dispersion medium, the criticality becomes apparent in developing fertilizer compositions having eutectic mixtures in water that satisfy both agronomic nutrient requirements and low temperature stability prevailing in a particular geographical location.